You may be aware that as per the Department of Telecom (DOT), Government of India roadmap for migration to IPv6 "All new registrations of .IN domain name is to be compulsorily on dual stack with effect from 1st January, 2014. The entire .IN domain should migrate to IPv6 (dual stack) latest by June 2014 as mandated by the Government.
Accordingly, .IN registry has extended support for connections to the registry hosts (EPP, WHOIS and Web) on IPv6 starting 15th May 2014 00:00 IST [14 May 2014, 18:30 UTC].
IPv6 subnets can be a combination of up to 3 subnets of /128, /64, /48. Registrars can submit IPv6 subnets as they see fit, as long as the total number of both IPv4 and IPv6 subnets stays within the limit of total 3 subnets.